we begin with the startling story of how u.s. soldiers were used as human guinea pigs. during the cold war, the military embarked on this top-secret program to test chemical and biological weapons. >> the researchers used animals, but believe it or not, they also used humans, volunteers from the army who had no idea what they were signing up for. nearly half a century later, some of these human guinea pigs, well, they're emerging from the shadows with disturbing stories about what the military did to them and how they're being treated now. dr. sanjay gupta investigates. ♪ >> i enlisted, joined at 18 years of age. it was the height of the vietnam war era and really felt a sense of duty to my country to go and serve. >> i went straight to ft. bragg. it was the thing to do. it was my duty as an american. >> i was drafted and i was placed in the 85th missile detachment. we were supposed to be security guards for the nuclear warheads that were going in missiles. >> reporter: three american soldiers, tim josephs, rank rochelle, bill blezinski called to arms from different b